Conventional ground sensors typically monitor an area of coverage, and report activity to a central location. Some conventional unmanned ground sensors are constructed so that they can be dropped from the air across a region of potentially hostile activity.
In contrast to manned vehicles which can employ expensive and mechanically complex gyroscopic compasses to facilitate navigation, unmanned ground sensors must be relatively small, durable and reliable since it is unlikely that the unmanned ground sensors individually can be conveniently retrieved and repaired. Rather, such unmanned ground sensors are typically distributed at stationary locations in the field in a sacrificial manner (i.e., with little or no intention of recovering and reusing the ground sensors due to hostile surroundings). Accordingly, such sensors are typically simple, low cost, remotely operational units.
One conventional unmanned ground sensor is equipped with an electronic magnetic compass that enables the ground sensor to determine the direction of the earth's magnetic north pole. The ground sensor is further equipped with a sensor assembly that detects activity in the vicinity of the ground sensor (e.g., general seismic activity, vehicle movement, human activity, etc.). When the ground sensor detects such activity, the ground sensor transmits data conveying the direction of that activity relative to the earth's magnetic north pole.